1.5 Cracking Flashcards
What is cracking?
The process of breaking down long chain alkanes into more useful shorter chains
What kind of cracking is used?
Thermal cracking
A variation of thermal decomposition
What does cracking include?
High heat
A catalyst
Describe the process of cracking
The long chain molecules are heated
They are vaporised
The vapour passes over a catalyst at a high temperature
The molecules are cracked on the surface of the catalyst
What can’t enter the reaction? Why?
Air
Because the oxygen reacts with the hydrogen and carbon to make H2O and CO2
What is the name given to the other hydrocarbon made in cracking?
Alkenes
What is the formula for an alkene?
C(n)+H(2n)
What do alkenes have that alkanes don’t?
At least one double bond
What does the double bond make the alkene?
Unsaturated
What bonds do alkenes have?
4 carbon bonds
1 hydrogen bond
At least one double bond between carbons
What is the chemical test for alkenes?
They will discolour bromine water from orange to colourless because the double bond reacts with the bromine water
Name the first 4 alkenes
Ethene
Propene
Butene
Pentene
What is polymerisation?
Many monomers join together to make a polymer
What is an alkene called in the plastics industry?
A monomer
What conditions are needed for polymerisation?
High heat
High pressure
A catalyst
What changes in the many monomers to make polymers?
The double bond breaks
What does each of the monomers: ethene, propene and styrene become in polymerisation?
Polyethene
Polypropene
Polystyrene
What chemical is added to polymers to make them into plastic?
Plasticisers
What are the problems with plastic?
Non-biodegradable
Non-renewable
Burning them produces CO2
What is a thermoplastic?
A plastic that can be heated and shaped into a new shape as it is melted down
What is a thermoset?
A plastic that will not change on heating
Example of a thermoset?
PVC pipes
What makes a thermoset and a thermoplastic different?
The strength of the bonds between polymers
What are biodegradable plastics made from?
Corn starch?
What is the advantage of biodegradable plastics?
Break down more easily
Renewable
What two ways can ethanol be produced?
Fermentation
Hydration of ethene
How do you get ethanol in fermentation?
Sugar -> ethanol + carbon dioxide
What are the advantages of fermentation?
Renewable
Uses little energy
Large quantities produced
What are the disadvantages of fermentation?
Increases food prices
Slow process
Ethanol needs to be purified in distillation
How do you get ethanol from hydration of ethene?
Ethene + steam (+catalyst) -> ethanol
What are the advantages of hydration of ethene?
Fast process
Continuous
Very pure ethanol
What are the disadvantages of hydration of ethene?
Non-renewable
Uses a lot of energy
High temperatures are needed
